Polymers were synthesized which contained pendent phosphonate ester or half-ester/half-acid groups. Some also contained pendent amine salt groups. Phosphonate groups have a high affinity for mineral surfaces and are expected to cause the polymer to be rapidly absorbed onto tooth surfaces from solution. One of the phosphonic acid/ester polymers (designated PPOBr phi P, J. Appl. Polym. Sci. 18:1969, 1974) was investigated for its adsorption characteristics on hydroxyapatite powder. It was found under conditions which neutralize the ionic charge of the acid groups, adsorption is enhanced: Increased concentration, pH valued below 7, strong electrolytes, and Ca ions all enhance adsorption. Viscosity was found to be markedly reduced below pH7 and upon addition of less than ionic-equivalent amounts of CaCl2. This indicates that the polymer conformation undergoes a change from an extended state, to a compressed state that occupies less volume when the phosphonic acid group charges are neutralized. It was also found that as polymer is adsorbed, phosphate ions are released into solution. The pattern of phosphate release as a function of adsorption time and of initial polymer concentration is consistent with a mechanism of adsorption in which phosphonate groups exchange with phosphate ions in the mineral surface. This mechanism was also supported by experiments which showed that phosphate solutions promote desorption and inhibit adsorption compared to KCl solutions of equivalent ionic strength. These experiments demonstrate that a layer of tenacious polymer can be rapidly applied from solutions of low concentration, and that a variety of controllable conditions influence the nature of the adsorbed layer. These results encourage the expectation that a material and a set of conditions can be found which can be used as a caries protective topical treatment.